Electrolysis of the aqueous solution of sodium chloride in an anode compartment results in an anolyte that contains active chlorine compounds. An anolyte obtained with a prescribed concentration of active chlorine is a disinfectant that is widely used in various fields for disinfection and sterilisation.
The disinfectants that are normally used have the active chlorine concentration of not more than 500-800 ppm, and in case of production with diaphragm electrolysis, approximately 1500 g active chlorine is obtained per hour per one device. With the increase in the output of electrolysis devices by up to 8000 grams per hour, the opportunities for the application of the anolyte become wider in industrial technologies that require disinfectants with the active chlorine concentration of 2000-6000 ppm. Furthermore, the existence of high output electrolysis devices gave the possibility of centralised disinfectant production and delivery to consumers. In order to reduce transportation costs, the disinfectants with a high concentration of active chlorine became highly in demand.
A known method for the production of disinfectants with a high active chlorine concentration, whereby the chlorine is obtained from the electrolyser as gas which is then dissolved in water, such as chlorine dioxide, is provided in U.S. Pat. No. 7,833,392 [1]. The disadvantage of this method is that it requires higher safety precautions on account of leaking gas, and inadequate dissolution of the gas in water—less than 2.9 g/l.
U.S. Pat. No. 7,897,023 [2] describes a method for obtaining a mixture of oxidants from an electrolyser, mainly gaseous chlorine with the following dissolution in water. Besides the certain efficiency of this method, the disadvantage of this method is that it requires higher safety precautions due to leaking gaseous chlorine and the complexity of hydraulic connections for the production of large quantities of disinfectant, since the electrolyser on which the method [2] is based has low productivity—only about 40 grams of active chlorine per hour. This method [2] is also complicated due to the need to use a circulation circuit and special external heat exchangers for the cooling of electrolytes.
There are methods for the production of disinfectant in a liquid state by means of an electrolyser. Such disinfectants include the known sodium hypochlorite which is obtained through electrolysis. The methods for its production are not viewed, because sodium hypochlorite is obtained in another type of electrolyser—an electrolyser without a diaphragm, therefore the method for the production of sodium hypochlorite is not comparable with the method presented herein.
A method for the production of disinfectant with an electrolyser by means of sodium chloride electrolysis with the output capacity of more than 600 grams of active chlorine per hour is possible on the basis of the description of electrolyser provided in U.S. Pat. No. 8,298,383 [3]. The disadvantage of patent [3] is that the reduction of flows passing through the electrode compartment for the purpose of producing disinfectants with active chlorine concentration of up to 2000 ppm causes the electrodes to heat up to 100° C.
Patent GB1396765 [4] describes a method for the production of disinfectant, wherein the heat of an anode as the inner electrode is lowered by passing coolant through a hollow inside the anode. The disadvantage of this method is its complexity due to the auxiliary external circulation circuit and a heat exchanger required for the cooling of the liquid.
Patent RU2350692 [5] describes a method, wherein the flow of electrolyte from the outside is channelled into a hollow in the anode, cooling it, and then flowing into the cathode compartment for producing the catholyte. The disadvantage of this method is that the method is not intended for the production of disinfectants and that the electrolyte enters the hollow in the anode from internal space through perforation in the anode wall, reducing the durability of the anode coating and the functioning order of the anode.
For the reduction of catholyte heating, the method of cooling by means of a Peltier element is also used in a known method (Thermoelectric Cooler—TEC), see e.g. patent JP2000051860 [6]. The disadvantage of this method is its low output caused by the low capacity of the Peltier element—up to 100 W·h, which allows taking out heat of no more than 4 liters per hour when producing disinfectants with active chlorine concentration of up to 6000 ppm.
In terms of embodiment and the achieved result, patent EE05608 [7] is the closest method, where the whole flow of water that passes into the electrolyser is initially divided into two parts: one part is guided into the cathode compartment, the second part is divided into two flows, one of which is guided into the anode compartment and the second flow is guided into an inner hollow in the cathode and then to the upper cover of the electrolyser for the purpose of diluting the anolyte to the required active chlorine concentration in the disinfectant, i.e. only part of the total water intended for the dilution of anolyte in the upper cover is guided to the cooling of the cathode. The active chlorine concentration in the anolyte before the anolyte reaches the upper cover of the electrolyser is up to 3000 ppm. This method [7] is regarded as the closest analogue. However, the disadvantage of this method, which was initially planned for the production of disinfectant at 500 ppm, is its limited capacity to yield disinfectants with high concentration, because the flow that is intended for the anode compartment enters the anode compartment, bypassing the inner hollow of the cathode, not participating in the cooling of the cathode and also not participating in the cooling of the catholyte, whereby the catholyte is only cooled by the flow that is intended for the reduction of active chlorine concentration in the disinfectant of less than 3000 ppm. However, with the need for production of disinfectants with active chlorine concentration of 3000 ppm, diluting the anolyte will no longer be necessary, i.e. the dilution flow that passes through the inner hollow of the cathode is stopped and only 2 flows will pass through the electrolyser: one flow through the cathode compartment, the other flow through the anode compartment, and method [7] becomes method [3] with a disadvantage that is related to the heating of electrolytes in the electrode compartments. As a result, application of method [7] in practice yields disinfectants with active chlorine concentration of no more than 2000 ppm, or cooling circulation circuits were to be used in order to obtain higher concentrations.